There was something I thought of a little while ago and it made me really curious.

My understanding is that all elements below a certain element, I think it is Iron (I could be wrong about the element) can undergo fusion. Once they reach iron, they are stable. I think it's suppose to be the most stable element or something. Also, things above that atomic number "fiz" down to or undergo fision and split apart till they reach iron.

Is this correct, or did I forget something I learned?

Okay, so if this is correct my second question is, can fusion of elements of high atomic number occur, if so, how?

And finally, if fusion cannot be forced for these higher elements that already exist how do we explain their existence? (My understanding is that the universe started out as all hydrogen I think and then fused together into the higher elements).

If I am off on any of these things along the way, (which I easily could be) then the later questions need not be answered.

The element is Iron (Fe56 to be specific)

Now it isn't that elements below this can't undergo fission, or that elements above it can't undergo fusion, only that it takes a net input of energy to make it happen.

So when a large sun dies, it is because it now longer can produce energy through fusion at its core. The sun collapses, the outer layers undergo a super fast fusion and the sun explodes into a supernova. Enough energy is then produced to force elements above iron to fuse, and we get the heavy elements.

I see, that would explain it. Thank you very much.

Has this process ever been observed? or is it theory?

oh ya, and since I love to look at cool equations so much if anyone would happen to know the equations that describe fusion/fision and could give a decent explanation of them that would be much appreciated.

Hi cephas1012,

"Has this process ever been observed? or is it theory?"

You are the living evidence that this process (fusion than higher than Fe56 elements) has ever happened. In the beginning of the universe, there only were light elements such as hydrogen and helium. Vast clouds of these elements collapsed to form the first stars. Once these stars start burning out, they do fuse elements higher than Fe56 (and insteading of producing energy they put energy in it), until they die in a nova or supernova. In the final stages of a star's life, it starts producing all kinds of high elements such as uranium, ... that gets blown away into deepspace as the nova or supernova occurs.

Out of the remnants of this nova or supernova, a new solar system can form, one like ours. These heavy materials are then responsible for the formation of rocky planets (remember the earth's iron core?), and the life it harbors.

So yes, the fact that you can mine uranium in Africa is an evidence that this process has once taken place.

"oh ya, and since I love to look at cool equations so much if anyone would happen to know the equations that describe fusion/fision and could give a decent explanation of them that would be much appreciated."

You should delve into nuclear physics, there are quite some nice introductory books around. I was tutored from Krane's "Introductory Nuclear Physics", but I would not recommend starting that book unless you know quantum mechanics, classical electromagnetism and special relativity. Nuclear physics requires some expertise in quite some fields of physics before you can properly understand it.

Bye!

Crisp

Hi Cephas1012,

Nuclear Physics is a very interesting topic in physics in my view, partly because it leads to and introduces you to particle physics and all those particles like photons, W and Z bosons, electrons neutrinos, etc...

Luckily (for reasons of simplicity), there are not many big equations to look at. You use E = mc^2 a lot (and it's relative cousin E = (gamma)mc^2). A couple of things you might want to look into is the Q-value of decay which lets you work out the energy released in fission.

Of course dealing with half-lives is not very hard so long as you are familiar with logarithms. Half-life = ln2/lambda which is derived from the equation of activity dN/dt = (dN/dt0)e^-lambda.t.

However cross-section for nuclei undergoing collisions during a reaction is interesting. I think it is something like R = R(initial)nto. Where n = number of molecules, t = thickness of cross-section, o = cross-sectional area of imaginary particles within the cross-section. Basically, you use this to work out the number of products (eg, no. neutrons in beta decay) produced after a reaction. Once again, look into this it is somewhat important.

Other than this, beginner-level nuclear physics does not get much more involved. As I said, using this knowledge is essential for the best understanding in particle physics where you study high-energy interactions between particles.

I hope this helps you.

Ben.

Originally posted by oxymoron
Hi Cephas1012,

Nuclear Physics is a very interesting topic in physics in my view, partly because it leads to and introduces you to particle physics and all those particles like photons, W and Z bosons, electrons neutrinos, etc...

Luckily (for reasons of simplicity), there are not many big equations to look at. You use E = mc^2 a lot (and it's relative cousin E = (gamma)mc^2). A couple of things you might want to look into is the Q-value of decay which lets you work out the energy released in fission.

Of course dealing with half-lives is not very hard so long as you are familiar with logarithms. Half-life = ln2/lambda which is derived from the equation of activity dN/dt = (dN/dt0)e^-lambda.t.

However cross-section for nuclei undergoing collisions during a reaction is interesting. I think it is something like R = R(initial)nto. Where n = number of molecules, t = thickness of cross-section, o = cross-sectional area of imaginary particles within the cross-section. Basically, you use this to work out the number of products (eg, no. neutrons in beta decay) produced after a reaction. Once again, look into this it is somewhat important.

Other than this, beginner-level nuclear physics does not get much more involved. As I said, using this knowledge is essential for the best understanding in particle physics where you study high-energy interactions between particles.

I hope this helps you.



Yes, this does help. thank you very much, and thank you to crisp.

I am actaully also very interested in particle physics. I did some reading on it a while ago. It had no math, just talked about the particles and ideas.

I have a question about half-life though. This is my understanding of the process of radioactive decay: The nucleus of an element like uranium is held together by the strong force. Within the nucleus the strong force over powers the EM force. However, if some neutrons and protons happened to venture outside a certain range, the EM force will be of greater magnitude then the strong force and the protons and neurtons will shoot away from the nucleus. This is alpha decay. Two protons, two neutrons--a helium nucleus. Now the reason that sometimes these alpha particles (if i can call them that, I am not sure) sometimes venture outside of the effective range of the strong force is because of quantum mechanics and uncertaintity and all. At least that is my understanding of it. Is this accurate so far? So my question comes in here. Can you use the wave equation to figure out the probabilty of alpha decay (helium necleus) occuring and does this work out to the half-life thing?

Enough energy is then produced to force elements above iron to fuse, and we get the heavy elements I had heard that the high velocities produced by the nova produce a particle-accelerator effect that produces these elements, much like we do in accelerators here, or would I be saying the same thing in a different way?

"Now the reason that sometimes these alpha particles (if i can call them that, I am not sure) sometimes venture outside of the effective range of the strong force is because of quantum mechanics and uncertaintity and all. At least that is my understanding of it. Is this accurate so far?"

Quite accurate. The alpha particle is normally trapped inside a potential well formed by the strong force, but it can tunnel through the Coulomb barrier that prevents it from escaping directly. Once the particle has tunneled, it is no longer subjected to the attractive strong nuclear force, but to the repulsive Coulomb force, ejecting the particle from the nucleus at high speed.

"So my question comes in here. Can you use the wave equation to figure out the probabilty of alpha decay (helium necleus) occuring and does this work out to the half-life thing?"

Well, you can surely calculate the tunneling probability (i.e. the probability of alpha decay) ... And I suppose that if you take a whole bunch of these particles that you can then retrieve the half-life exponential decay. I should look that up, but I don't have my books anywhere near me for the next two weeks.

Bye!

Crisp